Compact row decoder with multiple voltage support

ABSTRACT

The present invention provides a compact row decoder with multiple voltage support. The row decoder may include a global driver and a plurality of row-level drivers. The global driver may include one or more voltage level shifters that are operable to provide multiple voltages required to drive each of the plurality of row-level drivers. The plurality of row-level drivers each may include only one voltage level shifter. In an example, the row-level driver includes an address decoder implemented in a digital domain providing an address selection signal, a voltage level shifter to convert the address selection signal to an analog domain, and a tow driver receiving driving signals from the global driver. The row driver has no voltage level shifter contained therein. Thus, the row-level drivers and the row decoder may be very compact. The present invention further provides a CMOS image sensor including the row decoder and a method of operating the CMOS image sensor.

CROSS-REFERENCE TO RELATED U.S. APPLICATIONS

This application claims the benefit of U.S. Provisional PatentApplication No. 61/921,467, tiled Dec. 29, 2013, which is incorporatedherein by reference in its entirety.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not applicable.

NAMES OF PARTIES TO A JOINT RESEARCH AGREEMENT

Not applicable.

REFERENCE TO AN APPENDIX SUBMITTED ON COMPACT DISC

Not applicable.

FIELD OF THE INVENTION

The present invention generally relates to the technical field ofComplementary Metal-Oxide Semiconductor (CMOS) image sensor, and moreparticularly, to CMOS image sensor having a compact row decoder withmultiple voltage support.

BACKGROUND OF THE INVENTION

Consumer electronic products, for example, portable devices such assmart phones, pads, tablets, laptops and digital cameras, have beenrapidly developed and commercialized. To function as a digital camera,these smart phones, pads, tablets and laptops are typically equippedwith one or more camera modules to capture images or videos. Digitalcameras and camera modules can sense light using a semiconductor sensor,a common example of which is Complementary Metal-Oxide Semiconductor(CMOS) image sensor.

A CMOS image sensor includes a 2D (two dimension) array of pixelsarranged in rows and columns, and a row decoder to control operation ofthe pixels. The row decoder includes a plurality of row-level decoders,the number of which corresponds to the number of the pixel rows, andeach row-level decoder may drive a respective row of pixels. Therow-level driver often requires a plurality of high and low voltages forits operation. However, logic control signals are usually in a lowvoltage domain, which cannot serve directly as the required high and lowvoltages. To solve this problem, voltage level shifters are needed ineach row-level decoder to drive the high and low voltages.

As the resolution of the CMOS in sensor is continuously improved, thenumber of the pixel rows included in the CMOS image sensor increasesaccordingly. As a result, more and more row-level decoders are deployedin the CMOS image sensor to drive the pixel rows. These tow-leveldecoders consume a significant portion of the layout area and increasethe overall cost of the image sensor.

Therefore, there exists a need for a compact row decoder that is capableof providing multiple voltage support. Advantageously, the presentinvention provides a solution that can meet such a need. The approachesdescribed in this section are approaches that could he pursued, but notnecessarily approaches that have been previously conceived or pursued.Therefore, unless otherwise indicated, it should not be assumed that anyof the approaches described in this section qualify as prior art merelyby virtue of their inclusion in this section.

SUMMARY OF THE INVENTION

One aspect of the present invention provides a compact row decoder withmultiple voltage support. The row decoder comprises a plurality ofrow-level drivers configured to drive a plurality of rows of pixels; anda global driver comprising at least one global voltage level shifterthat is operable to drive the plurality of row-level drivers. In anembodiment, the plurality of row-level drivers each comprises an addressdecoder and a row driver.

In an exemplary embodiment, a row decoder may include a global driverand a plurality of row-level drivers that correspond to a plurality ofrows of pixels. The global driver may include one or more voltage levelshifters that are operable to provide multiple voltages required todrive each of the plurality of row-level drivers. The plurality ofrow-level drivers may each include only one voltage level shifter.

In an example, each row-level driver may include an address decoder, avoltage level shifter and a row driver. The address decoder isimplemented in a digital domain and operates to provide an addressselection signal. The voltage level shifter may convert the addressselection signal to an analog domain. The row driver may receive theconverted address selection signal from the voltage level shifter anddriving signals from the global driver. Although the row driver isimplemented in the analog domain, it has no voltage level shiftercontained therein. Thus, the row-level drivers and the row decoder maybe very compact.

Another aspect of the invention provides a CMOS image sensor. The sensorcomprises a plurality of rows of pixels and a row decoder. The rowdecoder comprises a plurality of row-level drivers configured to drivethe plurality of rows of pixels; and a global driver comprising at leastone global voltage level shifter that is operable to drive the pluralityof row-level drivers.

Still another aspect of the present invention provides a method foroperating a CMOS image sensor. The CMOS image sensor comprises aplurality of rows of pixels, a row decoder, and a global driver. The rowdecoder comprises a plurality of row-level drivers provided for theplurality of pixel rows, respectively. The method comprises a step ofgenerating, by the global driver, voltages in an analog domain requiredfor operation of the row-level drivers; and a step of providing thevoltages in the analog domain from the global driver to the row-leveldrivers.

The above features and advantages and other features and advantages ofthe present invention are readily apparent from the following detaileddescription of the best modes for carrying out the invention when takenin connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The present invention is illustrated by way of example, and not by wayof limitation, in the figures of the accompanying drawings and in whichlike reference numerals refer to similar elements. All the figures areschematic and generally only show parts which are necessary in order toelucidate the invention. For simplicity and clarity of illustration,elements shown in the figures and discussed below have not necessarilybeen drawn to scale. Well-known structures and devices are shown insimplified form such as block diagrams in order to avoid unnecessarilyobscuring the present invention. Other parts may be omitted or merelysuggested.

FIG. 1 is a block diagram schematically showing a row decoder inaccordance with an exemplary embodiment of the present invention.

FIG. 2 depicts a circuit diagram for a row driver and a pixel coupledthereto in accordance with an exemplary embodiment of the presentinvention.

FIG. 3 is a circuit diagram for a row address decoder with a voltagelevel shifter in accordance with an exemplary embodiment of the presentinvention.

FIG. 4 shows a circuit diagram for a global driver with voltage levelshifters in accordance with an exemplary embodiment of the presentinvention.

FIG. 5 is a block diagram showing a CMOS image sensor in whichembodiments of the present invention may be implemented.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In the following description, for the purposes of explanation, numerousspecific details are set forth in order to provide a thoroughunderstanding of the present invention. It is apparent, however, to oneskilled in the art that the present invention may be practiced withoutthese specific details or with an equivalent arrangement

It is also to be understood that the terminology used herein is for thepurpose of describing particular embodiments only, and is not intendedto limit the scope of the invention. For example, when an element isreferred to as being “on”, “connected to”, or “coupled to” anotherelement, it can be directly on, connected or coupled to the otherelement or intervening elements may be present. In contrast, when anelement is referred to as being “directly on”, “directly connected to”,or “directly coupled to” another element, there are no interveningelements present.

Unless otherwise defined, all terms (including technical and scientificterms) used herein have the same meaning as commonly understood by oneof ordinary skill in the art to which this present invention belongs. Itwill be further understood that terms, such as those defined in commonlyused dictionaries, should be interpreted as having a meaning that isconsistent with their meaning in the context of the relevant art andwill not be interpreted in an idealized or overly formal sense unlessexpressly so defined herein.

Below, respective embodiments will he described in details by referenceto the accompanying drawings. Incidentally, in all the drawings fordescribing the embodiments, the elements having the same function aregiven the same reference signs and numerals, and a repeated descriptionthereon is omitted. Further, in the following embodiments, a descriptionon the same or similar portions will not be repeated unless otherwiserequired.

The compact row decoder of the present invention can significantlyreduce the layout area thereof, when it provides multiple high and lowvoltage support. It also provides the flexibility to add additionallogic functions at low cost of the layout area.

FIG. 1 is a high level block diagram showing a row decoder 100 inaccordance with an exemplary embodiment of the present invention.Referring to FIG. 1, the row decoder 100 includes two main parts, i.e.,a row level driver 10 and a global driver 20. Although not shown, theremay be a plurality of row level drivers 10 that serve to drive aplurality of rows of pixels, respectively. Only one global driver 20serves to drive the plurality of row level drivers 10.

Each of the row level drivers 10 may further contain two majorsub-blocks, i.e., an address decoder 30 and a row driver 50. The addressdecoder 30 may he implemented in a digital domain, e.g., using a lowvoltage digital power supply and digital core Metal-Oxide SemiconductorField Effect Transistors (MOSFETs). The row driver 50 may be implementedin an analog domain, which uses high and low voltage supplies asrequired. Since the address decoder 30 and the row driver 50 areincluded in the row level driver 10, they both are repetitively providedfor the plurality of pixel rows, thereby costing a significant portionof the layout area.

In the embodiment, the high and low voltage supplies requited in the rowdriver 50 may be provided by the global driver 20. Specifically, theglobal driver 20 may include at least one global voltage level shifter(not shown) to convert driving signals from the digital domain to therequired analog domain. Thus, the row driver 50 does not need anyvoltage level shifter contained therein. The row level drivers 10 mayinclude only one low-to-high buffer, i.e., the voltage level shifter 40connected between the address decoder 30 and the row driver 50 as shownin FIG. 1. The voltage level shifter 40 may convert a digital voltage toa highest swing control voltage, which will be discussed in more detailslater.

Although the at least one voltage level shifter circuit is stillrequired in the global driver 20, and it needs relatively large buffersto drive all the row level driver circuits, it still costs much smallerlayout area than putting the voltage level shifter into each row,because it only repeats one time, not as many times as the row leveldrivers 10 repeat. The low-to-high voltage level shifter 40, which maybe a one-bit buffer provided in each of the plurality of row leveldrivers 10, costs some layout area, but it is much less than multiplein-row voltage level shifters that are otherwise provided in each rowlevel driver 10. The address decoder 30 provided in each row leveldriver 10 uses a low voltage, which enables it to use the smallestdigital MOSFETs. As a result, more complex address decoding logics canbe implemented in this sub-block without adding a large layout area.Based on the above structures, the overall layout area of the rowdecoder 100 would be very compact.

FIG. 2 illustrates a circuit diagram of the row driver 50 and one of thepixels 110 driven by the row driver 50, in accordance with an exemplaryembodiment of the present invention. As a typical pixel for a CMOS imagesensor, the pixel 110 has three major inputs, i.e., a reset signal RST,a transfer signal TX, and a row selection signal RS. Each input mayrequire a high voltage and a low voltage. The row driver 50 may includethree identical logic and driving structures for each of the three inputsignals, i.e., a channel 52 for the reset signal RST, a channel 54 forthe transfer signal TX, and a channel 56 for the row selection signalRS.

Referring to FIG. 2, the channel 52 for the reset signal RST may includean AND gate 120 and an inverter 130. The AND gate 120 receives anaddress selection signal ADD_SEL_H, which has been converted by thevoltage level shifter 40 to a highest swing control voltage, and a resetcontrol signal RST_H provided from the global driver 20. The output ofthe AND gate 120 is connected to an input of the inverter 130. Thus, thechannel 52 for the reset signal RST may determine the output signal RSTon the basis of the address selection signal ADD_SEL_H and the resetcontrol signal RST_H. The channel 54 for the transfer signal TX mayinclude an AND gate 140 and an inverter 150. The AND gate 140 receivesthe address selection signal ADD_SEL_H and a transfer control signalTX_H provided from the global driver 20. The output of the AND gate 140is connected to an input of the inverter 150. Thus, the channel 54 forthe transfer signal TX may determine the output signal TX on the basisof the address selection signal ADD_SEL_H and the transfer controlsignal TX_H. The channel 56 for the row selection signal RS may includean AND gate 160 and an inverter 170. The AND gate 160 receives theaddress selection signal ADD_SEL₁₃ H and a row selection control signalRS_H provided from the global driver 20. The output of the AND gate 160is connected to an input of the inverter 170. Thus, the channel 56 forthe row selection signal RS may determine the output signal RS on thebasis of the address selection signal ADD_SEL_H and the row selectioncontrol signal RS

As shown in FIG. 2, when the address selection signal ADD_SEL_H is high,it means that this row of pixels is selected for access; when it is low,it means that this row of pixels is in a non-access status. The resetcontrol signal RST_H, the transfer control signal TX_H and the rowselection control signal RS_H may further determine only a portion ofthe time the pixels 110 in the row are accessible.

All the input signals, ADD_SEL_H, RST_H, TX_H, and RS_H, have alreadybeen converted to the highest swing voltage domain, and all the logicgates and inverters involved here, i.e., the AND gates 120, 140, 160 andthe inverters 130, 150, 170, are powered by its related high and lowvoltages. The high voltages for V_RST_High, V_TX_High and V_RS_High mayhe the same or different, and the low voltages for V_RST_Low, V_TX Lowand V_RS_Low may be the same or different. In any condition, the inputsignals ADD_SEL_H, RST_H, and RS_H should have been converted to thehighest voltage range, i.e.,

V_input_High=max (V _(—) RST_High,V _(—) TX_High,V _(—) RS_High);

V_input_Low=min(V _(—) RST_Low,V _(—) TX_Low,V _(—) RS_Low).

As can be seen, since all the input signals ADD_SEL_H, RST_H, and RS_Hhave been converted to the highest voltage range, the row driver 50 maynot have any voltage level shifter contained therein. Thus, the layoutarea cost by the row driver 50 may he greatly reduced, especiallyconsidering that one row driver 50 is provided for each row of pixels.In addition, the address selection signal ADD_SEL_H, the reset controlsignal RST_H, the transfer control signal TX_H and the row selectioncontrol signal RS_H will be discussed in more detailing later.

Further referring to FIG. 2, the pixel 110 may operate with the resetsignal RST, the transfer signal TX and the row selection signal RS. Asshown, the pixel 110 may include a typical 4T (four transistor)structure, i.e., a transfer transistor Mtx, a rest transistor Mrst, asource-follower readout transistor Msf, and a row selection transistorMrs. The pixel 110 may further include a photodetector such as aphotodiode PD, and the photodiode PD may sense light and convert lightinto charges. When the transfer transistor Mtx turns on, the charges maybe transferred to a floating diffusion (FD) region. The readouttransistor Msf may act as an amplifier which allows the pixel voltage tobe observed without removing the accumulated charges in the FD region.The row select transistor Mrs allows a single row of the pixel array tobe read by the read-out electronics via the pixel signal bus. The resettransistor Mrst acts as a switch to reset the floating diffusion region.When the reset transistor turns on, the FD region is effectivelyconnected to the power supply Vdd, clearing all accumulated charges.

It would be apparent that the present invention is not limited to anyspecific structure of the pixel 110 or the pixel array of the CMOS imagesensor. The embodiments set forth here are also applicable to pixelshaving other structures, such as Noble 3T pixels and 5T or 6T pixels.The same effects may also be achieved in such pixels by applying theembodiments as disclosed here.

Referring now to FIG. 3, there shows a circuit diagram for a row addressdecoder 300 and a one-bit voltage level shifter 310 in accordance withan exemplary embodiment of the present invention. The row addressdecoder 300 may be used as the address decoder 30 as shown in FIG. 1,and the one-bit voltage level shifter 310 may be used as the voltagelevel shifter 40 as shown in FIG. 1.

As shown in FIG. 3, the row address decoder 300 may include digitallogic gates 320. 330, 340 and 350. The logic gates 320, 330 and 340 maybe NAND gates which have their inputs connected to the address linesA<n:0> (A<8:0> in this example), and the logic gate 350 may be a NORgate which has its inputs connected to the outputs Of the NAND gates320, 330 and 340. It would be apparent that in other embodiments, therow address decoder 300 may include more or less digital logic gates,depending on the number of the rows included in the pixel array.

Only when all the address lines A<0> to A<n> are at a high level, theoutput of the NOR gate 350, i.e., the digital row selection signalADD_sel_D, can be at a high level, which means the row that correspondsto the row address decoder 300 is selected for access. All the logicgates 320, 330, 340 and 350 included in the row address decoder 300 mayuse low voltage digital core MOSFETs, which occupy a very small layoutarea. Since the basis layout area is in a pure digital domain, it isalso very easy to add additional row level logic functions, for example,adding a latch or additional logic elements, without adding a lot oflayout area cost.

The digital signal ADD_sel_D may be provided from the row addressdecoder 300 to the input of the one-bit voltage level shifter 310, whereit is converted to a high voltage range signal ADD_SEL_H that is highenough to drive the row driver circuit 50. Referring to FIG. 3, theone-bit voltage level shifter 310 may be implemented as a typicalvoltage level shifter circuit that includes a digital domain inverter360 and a cross-coupled inverting pair composed of MOSFETs 400, 410,420, 430, 440 and 450. Specifically, the PMOS transistor 400, the PMOStransistor 410 and the NMOS transistor 420 that are connected in seriesin this order are parallel with the PMOS transistor 430, the PMOStransistor 440 and the NMOS transistor 450 that are connected in seriesin this order between a power supply Vddh and the around GNDa. The gateof the PMOS transistor 400 is connected to a connecting point betweenthe PMOS transistor 440 and the NMOS transistor 450, and a gate of thePMOS transistor 430 is connected to a connecting point between the PMOStransistor 410 and the NMOS transistor 420. The digital signal ADD_sel_Dis provided to the gate of the PMOS transistor 410 and the NMOStransistor 420 and to the input of the inverter 360, and the output ofthe inverter 360 is provided to the gate of the PMOS transistor 440 andthe NMOS transistor 450. The output signal ADD_SEL_H is extracted fromthe connecting point between the PMOS transistor 440 and the NMOStransistor 450.

The digital input signal ADD_sel_D goes into the digital domain inverter360 first, and then the input and output of the inverter 360 drive thecross-coupled inverting pair 400-450 in a high voltage domain, therebygenerating the output signal ADD_SEL_H. Thus, the address selectionsignal ADD_SEL_H has been converted to the highest swing control voltageby the voltage level shifter 310, and it becomes high enough to drivethe row driver 50. It would be apparent that the voltage level shifter310 may also use any other structures. Again, the address decoder 300(or 30) is implemented in the digital domain, and it includes no voltagelevel shifter. Although the row driver 50 is implemented in the analogdomain, it does not include any voltage level shifter either. Asdiscussed below, the row driver 50 may acquire driving signals in theanalog domain from the global driver 20. Therefore, the row level driver10 may include only one voltage level shifter, i.e., the voltage levelshifter 40 (or 310), and thus it may be built very compact.

FIG. 4 shows a circuit diagram for the global driver 20 with voltagelevel shifters in accordance with an exemplary embodiment of the presentinvention. Again, the global driver 20 does not need to repeat as therow level driver 10 does. Referring to FIG. 4, the global driver 20 mayinclude a plurality of digital voltage domain inverters 500, 510, 520and 530 that form a driver for address signals Address<n:0>(Address<8:0> in this example). The plurality of digital voltage domaininverters 500, 520 and 530 convert the digital address signalAddress<8:0> into complementary signals A<8:0> and NA<8:0> for easyconnection in the row level address decoder 300. As discussed above, theaddress decoder 300 may be implemented in the pure digital domain, sothere is no need to convert voltage domain for the address signals.

For other control signals RST_H, TX_H and RS_H, however, voltageconversion is necessary because the row driver 50 is implemented in theanalog domain as disclosed above. Specifically, the global driver 20 mayinclude a first global voltage level shifter 540, a second globalvoltage level shifter 570, and a third global voltage level shifter 600.An input signal RS_D, which is in a low voltage digital domain, firstlygoes to the first global voltage level shifter 540 where it is convertedto an RS_High/RS_Low domain. Then, the output from the first globalvoltage level shifter 540 passes through the inverters 550, 560 in anRS_High/RS_Low power supply domain to output the driving signal RS_H.The first global voltage level shifter 540 may use the same structure asthe voltage level shifter 310 shown in FIG. 3, or any other suitablestructures. Similarly, the other two signals RST_D and TX_D can utilizethe same voltage level shifting and inverter buffering structure as thesignal RS_D does. Referring to FIG. 4, the digital control signal RST_Dmay be processed in a channel composed of the second global voltagelevel shifter 570 and following inverters 580, 590, thereby generatingthe driving signal RST_H. The digital control signal TX_D may beprocessed in a channel composed of the third global voltage levelshifter 600 and following inverters 610, 620, thereby generating thedriving signal TX_D. Please note that the voltage level shifters 540,570 and 600 may be in different voltage levels in differentapplications, or under different requirements. As such, the controlsignals have been converted from the digital domain to the analog domainwhen they are provided to drive the row driver 50. So, the row driver 50does not need to include any voltage level shifter. In addition, due tothe simple structure of the global driver 20 as described above, itslayout size can be very small too.

FIG. 5 depicts a block diagram showing a CMOS image sensor 700 in whichembodiments of the present invention may be implemented. Referring toFIG. 5, the CMOS image sensor 700 may include a pixel array 720. Thepixel array 720 may include a plurality of pixels arranged in rows andcolumns, and each of the plurality of pixels may be the same as orsimilar to the pixel 110 as shown in FIG. 2.

The pixel array 720 may be driven by the row decoder 100 as previouslydiscussed with reference to FIGS. 1-4 and a column decoder 710, and animage signal generated by the pixel array 720 may be extracted by asampling circuit 730 and be further processed by a processing circuit(not shown).

An embodiment for the method of operating the CMOS image sensor 700 willbe described herein with reference to FIGS. 1-5. Specifically, themethod may include generating, by the global driver 20, voltages in theanalog domain required for operation of the plurality of row-leveldrivers 10, and providing the voltage in the analog domain from theglobal driver to the plurality of row-level drivers 10. In particular,the voltages in the analog domain may be used to drive the row driver 50that is included in each of the row-level drivers 10. In an example, thevoltages in the analog domain may be generated by one or more voltagelevel shifters converting the voltages from the digital domain to theanalog domain. In such a case, the driving voltages requited for the rowdriver 50 has been converted into the analog domain by the global driver20 when they are provided to the row driver 50. The row-level driver 10may include only one voltage level shifter 40 that converts the addressselection signal ADD_sel_D in the digital domain provided from theaddress decoder 30 to the address selection signal ADD_SEL_H in theanalog domain so that it can be used directly by the row driver 50.Consequently, the row driver 50 itself does not need any voltage levelshifter.

In the foregoing specification, embodiments of the present inventionhave been described with reference to numerous specific details that mayvary from implementation to implementation. The specification anddrawings are, accordingly, to be regarded in an illustrative rather thana restrictive sense. The sole and exclusive indicator of the scope ofthe invention, and what is intended by the applicant to be the scope ofthe invention, is the literal and equivalent scope of the set of claimsthat issue from this application, in the specific form in which suchclaims issue, including any subsequent correction.

1. A row decoder, comprising: a plurality of row-level drivers (10) configured to drive a plurality of rows of pixels; and a global driver (20) comprising at least one global voltage level shifter that is operable to drive the plurality of row-level drivers.
 2. The row decoder according to claim 1, wherein each of the plurality of row-level drivers comprises an address decoder (30) and a row driver (50).
 3. The row decoder according to claim 2, wherein the address decoder is implemented in a digital domain, and wherein the row driver is implemented in an analog domain.
 4. The row decoder according to claim 2, wherein the at least one global voltage level shifter is configured to provide driving signals in an analog domain to the row driver.
 5. The row decoder according to claim 2, wherein the row driver has no voltage level shifter included therein.
 6. The row decoder according to claim 2, wherein the plurality of row-level drivers each further comprises a row-level voltage level shifter connected between the address decoder and the row driver.
 7. The row decoder according to claim 6, wherein the row-level voltage level shifter is configured to convert a row access signal from a digital domain to an analog domain.
 8. The row decoder according to claim 6, wherein the plurality of row-level drivers each comprises only one row-level voltage level shifter.
 9. The row decoder according to claim 2, wherein the at least one global voltage level shifter further comprises: a first global voltage level shifter configured to convert a reset control signal from a digital domain to an analog domain; a second global voltage level shifter configured to convert a transfer control signal from the digital domain to the analog domain; and a third global voltage level shifter configured to convert a row selection control signal from the digital domain to the analog domain, wherein the reset control signal, the transfer control signal and the row selection control signal in the analog domain are provided to the row driver.
 10. The row decoder according to claim 9, wherein the row driver comprise: a reset channel configured to receive the reset control signal and generate a reset signal for a reset operation of a pixel; a transfer channel configured to receive the transfer control signal and generate a transfer signal for a charge transfer operation of a pixel; and a read channel configured to receive the row selection control signal and generate a row selection signal for a read operation of a pixel.
 11. A CMOS image sensor, comprising a plurality of rows of pixels; and a row decoder, wherein the tow decoder comprises a plurality of row-level drivers (10) configured to drive the plurality of rows of pixels; and a global driver (20) comprising at least one global voltage: level shifter that is operable to drive the plurality of row-level drivers.
 12. The CMOS image sensor according to claim 11, wherein the plurality of row-level drivers each comprises an address decoder (30) and a row driver (50).
 13. A method for operating a CMOS image sensor, the CMOS image sensor comprising a plurality of rows of pixels and a row decoder, the row decoder comprising a plurality of row-level drivers provided for the plurality of pixel rows, respectively, and a global driver, the method comprising: generating, by the global driver, voltages in an analog domain required for operation of the row-level drivers; and providing the voltages in the analog domain from the global driver to the row-level drivers.
 14. The method according to claim 13, wherein the row-level drivers each comprise an address decoder implemented in a digital domain and a row driver implemented in the analog domain, and wherein the step of providing the voltages comprises providing the voltages in the analog domain to the row driver.
 15. The method according to claim 14, wherein the step of generating the voltages comprises converting, by at least one voltage level shifter included in the global driver, the voltages from the digital domain to the analog domain.
 16. The method according to claim 14, wherein the row driver has no voltage level shifter included therein.
 17. The method according to claim 14, further comprising: generating, by the address decoder, a row access signal in the digital domain; and converting, by a row-level voltage level shifter connected between the address decoder and the row driver, the row access signal from the digital domain to the analog domain.
 18. The method according to claim 14, wherein the plurality of row-level drivers each comprise only one voltage level shifter. 